Aircraft fuel pump



Jan. 6, 1942.

R. B. CURTIS AIRCRAFT FUEL PUMP Original Filed July 13, 1939 Z WI EWZQP'Russel! I'B. Cur h 5 Patented Jan. 6, 1942 AIRCRAFT FUEL PUMP Russell E.Curtis, Dayton, Ohio, assignor to Ourtis Pump Company, Dayton, Ohio, acorporation of Ohio Original application July 13, 1939, Serial No.

Divided and this application March 8, 1941, Serial N0. 382,315

3 Claims.

This invention is a division of my copending application, Serial No.284,263, filed July 13, 1939, and relates to aircraft fuel pumps andmore particularly to mechanism for maintaining at a constant value thepre-selected pressure on the discharge side of the pump.

Due to the fact that fuel tanks in aircraft are usually remotely locatedwith respect to the fuel pump, it is inevitable that the various angleswhich the craft assumes in flying frequently alter the suction head onthe intake side of the pump. Unless compensated for, this rise and fallin the suction head constantly influences the discharge pressure of thepump as regulated by the relief valve.

It is therefore an object of this invention to provide simple yetaccurate compensating means whereby the negative loading of the reliefvalve due to increased suction on the low side will not affect. thepressure .on the discharge side for which the valve has been adjusted.

Another object of this invention is the provision of balancing means fora relief valve structure whereby variation in the suction does not addto or subtract from the forces tending to open the valve and thereforedoes not affect the discharge pressure of the fuel pump.

The novel features believed to be characteristic of the presentinvention are set forth with particularity in the appended claims. Theinvention itself, however, both as to its organiza- (not shown) forrotatlvely supporting a rotor 26. The rotor is transversely slotted toslidably receive the three through blades 34, the cylinder bore and endsof the blades being so formed that the blade ends contact the cylinderwall at all points in their rotation. I

The cylinder 20 has slots 36 and 38 positioned to align with ports 40and 42 in the body I2.

With rotation in the direction of the arrow '44, Figure 1, 40 becomesthe suction port and 42 the discharge port, but by merely removing thescrews (not shown) that connect the valve body I06 to the pump body I2and turning the entire relief and by-pass valve structure through anangle of 180 on its vertical axis and reconnecting the valve and pumpbodies, the pump will be adapted for rotation in a direction opposite tothat of the arrow 44 whereupon 42 is the suction port and 40 thedischarge port. No other change is required. Opposite hubs 48 are pipethreaded as at 49 for suction or discharge pipesas required. 4

A-suitable driving mechanism (not shown) is provided for drivingconnection with the rotor 26.

tion and manner of construction, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in connection withthe accompanying drawing, in which:

Figure 1 is a vertical cross-sectional view, with parts in elevation, ofa fuel pump, illustrating the details of construction of th diaphragmand valve spring cup when the latter is at its lowermost limit ofmovement as taught by the present invention;

Figure 2 is a transverse cross-sectional view taken substantially in theplane of the joint indicated by the broken line IIII of Figure 1; and

Figure 3 is a fragmentary cross-sectional view of the diaphragm andvalve spring cup arrangement similar to Figure l but showing therelation of parts when the cup is actuated to its uppermost limit ofmovement.

' As best shown in Figure l, the pump body I2 is bored intermediate itsends and concentrically supports the eccentrically bored pump cylinder28 and is provided with front and rear journals The relief valvestructure provided for maintaining the discharge pressure at a constantvalue is housed in the valve body I06 which is suitably secured to thepump body by means of screws or the like, and a valve head I08 securedto the main valve body I06 by the screws H0. 7

The relief valve proper is of the poppet type comprising the disk. II2with stem II4 slidable in a hub I it of the main body I06, the diskbeing beveled at I I8 and having a corresponding angular seat in thebody which divides the interior of the body I06 into a suction chamberI20 including all of the space above the disk H2 and a discharge chamberI22 below the disk.

Ducts I24 and I26 in the pump and valve bodies, respectively, connectthe suction port 40 to the suction chamber I20, while ducts I28 and I30in the valve body and pump body respectively connect the dischargechamber I22 to the discharge port 42.

- Depending from the valve head I08 into the suction chamber I20 is along hub I32 internally chambered to contain a valve loading spring I84and externally sized to slidably receive a valve spring cup I36, thebottom of which rests upon a small knob I38 on the upper side of thevalve disk H2.

The valve spring adjusting means comprises an. adjusting screw I40 witha head I42 and a flange I44 intermediate the screw and head, the flangebeing of larger diameter than the headlower adjust! screw retainingwasher Hi6 rests on a shoulder H03 and has a central opening throughwhich the screw extends freely, the flange 5 resting on the upper faceof the washer. The upper retaining washer I50 has a central o 'ng whichpasses over the screw head is 100: 'ld rests on the flange I44. A springring 452 is snapped into a groove at the upper edge of the Washer 551i,the groove being positioned to hold the two washers so spaced as toallow free turning movement of the flange I44 between them. A springadjusting nut is tapped to fit the external threads of the screw I40 andhas a peripheral key extending laterally into a keyway (not shown) onthe valve head I08,

I not shown) similar to the key on the spring ad justing nut I56 andwhich extends into a keyway in the valve head I08 to hold the washer I50from rotating.

The adjusting screw cap I10 when drawn against the spring to open thevalve would be the discharge pressure, acting to raise the valve frombelow, plus the suction tending also to raise it but from above. Valvesfor use inthis situation are therefore provided with a balancing meanswhereby variation in the suction does not add to nor subtract from theforces tending to open the valve, and therefore does not affect thedischarge pressure. The release valve balancing means herein providedcomprises a diaphragm I14 of resilient synthetic rubber preferably withan intightly to the gasket I12, allows but a slight v clearance betweenthe inside of the cap andthe' top of the locking bar W2 whereby theba'ris retained in the notch in which-it has been placed as long as thecap is in position.

When an adjustment of the spring I34 is to be made, the cap IHi is firstremoved, then, by the simple insertionof a screwdriver into the slotI60, the locking bar I62 is made to rise out of the notch in the washerI50 and the screw may be rotated until the desired adjustment isobtained, whereupon the locking bar is pushed into the nearest notch andthe cap I10 replaced. In a situation where it may be necessary to reachinto close spaces to make this adjustment, the desirability of thissimple manipulation is obvious.

Furthermore, where height is limited. as it is on pumps of this class, asmall portion only of the available height is taken by the adjusting andlocking means, leaving space for a longer and more flexible spring,whereby larger increments of adjustment may be made with smallerresulting variations in spring stress making the matter of adjusting forfine variation in discharge pressure not dependent upon skillful orcareful manipulation of the adjusting means. The use of a longer andmore flexible spring also results in less variation in the dischargepressure at the various speeds of rotation and rate of dischargeencountered in the operation of aircraft.

Now, as is well known in the art, the suction head against which thepump operates varies from one instant to the next because of aircraftacceleration. or deceleration, or altitude, orthe fact that the fueltank, when the aircraft climbs,

may be well below the pump. and when it dives it may be well above it,or vice versa, all depending upon the respective locations of the pumpand tank. Consequently, if an ordinary springloaded release valve onlywere provided, this changing rise and fall of the pressure in chamberi520 would cause the discharge pressure to fluctuate, because of the sumtotal of the force acting ternal fabric layer (not shown) to give itadditional strength. Around the edge of the central opening the materialis thickened to provide a ring I16 around which the upper edge of thespring cup I36 is so closely rolled as to form an airtight joint at thispoint, and prevent the cup and diaphragm from pulling apart inoperation.

The diaphragm is also made thicker at the outer edge to form the wedgingring I18, this ring and a small portion of the diaphragm being clampedbetween the valve body I06 and the valve head I08.

Since the material of the diaphragm is subject to cold flow underexcessive pressure, the space between the body I06 and head I 08, whichcontains the outer edge, must be carefully made so thatwhen metal tometal contact of the body and head is made at I80, the diaphragm will begripped tight enough to safely prevent pulling out under the suctionpressure in operation, but not tight enough to cause cold flow.

The active portion I82 of thevdiaphragm is of U shaped cross sectionwhich loops downward between the outside of the cup I36 and the inneredge of the annular rib I84 in the body I 06.

Since the material composing the diaphragm swells'appreciably fromgasoline absorption, the loop I 82 will drop downward more as thematerial swells. It will also be drawn upwardly farther as the valverises to its maximum height. If then, the effective area of thediaphragm is to remain constant under both of these extremes, the sidesof the U loop must be so supported as to maintain a constant width underall conditions.

This condition will be met when the drop in the loop I82 and the widthof the rib I84 is such that the sides of the loop will be held paralleland to a uniform spacing with each other in all positions. In suchastructure, the effective area of the diaphragm will be constant for anyvalve lift and for any degree of swelling of the material, and thedischarge pressure will be unaffected by these variations.

The relative positions of parts at the extreme limits of movement of thevalve spring cup I30 are best illustrated in Figures 1 and 3.- As shownin Figure 1, the valve spring cup I36 is at its lowermost limit ofmovement in which it rests on the knob I38 of the valve disk I I2. InFigure 3, the valve spring cup I36 is illustrated as abutting the end ofthe chamber I86 in which it is in its uppermost limit of movement.

The diaphragm I14 is so shaped and positioned that the valve disk I I2may rise to its maximum operating height a distance of approximately ofan inch without causing change in the effective area of the diaphragm.The loop I82 of the diaphragm remains exposed to the suction chamher I20as the valve disk H2 is raised and lowered. As the valve spring cup I36rises, it effects a rolling action of the diaphragm loop I 82 in such amanner that the effective area thereof remains substantially constant.

the tapped opening I90, causing the fuel discharge pressure to increasedirectly with rise in manifold pressure.

Obviously, increased suction inthe chamber i20 will pull as much cup I36as it does upwardly on the valve disk H2, and the valve closing pressurewill be controlled entirely by the spring I34 independently ofvariations in suction heads A by-pass valve is usually incorporated inthe relief valve body of the power pump of aircraft fuel systems, sothat, in the event of sticking of the power pump rotor, or otherpowefmump failure, fuel may be forced through the power pumpindependently of its coupling elements, by means of an auxiliary handpump provided for the purpose.

Heretofore, these by-pass valves have been made with ametal to metalseat, necessitating considerable initial spring pressure .to hold themclosed when not operating, and have not been so placed as to provide thegreatest freedom in the passages through them, whereby considerable handpump efiort was required to overcome these innate resistances beforehand pumping became effective. I

The by-pass valve I92 herein disclosedis of synthetic rubber to metalseat construction so that a very light spring holds it closedeffectively against leakage, and it is so placed and its orifices soshaped, as to provide a substantially direct non-resisting passage forthe flow of'the hand pumped fuel.

While the constructions of the locking arrangements for the adjustablespring, the rotary main pump and the by-pass valves have been describedin more or less greater detail, it is to be understood that suchconstructions form no part of the invention claimed herein and areillustrated and described only for the purpose of more clearlydefiningtheir coaction in relation to. the adjustable spring cup anddiaphragm. Any other types ofconstructions with the adjustable springcup and diaphragm in a like manner may be used equally as well.

While a particular embodiment only of this invention has beenillustrated, it will, of course, be understood that the invention shouldnot be limited thereto, since many modifications may be made and,therefore, it is contemplated by the appended claims to cover all suchmodifica harder downwardly on the tubular portion said housing, a

which would coact 3 tions as fall within the true spirit and scope ofthe present invention.

I claim as my invention: 1. A diaphragm construction comprising a pairof spaced relatively movable members, a flexible diaphragm extendingbetween the members and having legs adapted members and away from themembers are moved-#relative to each other for maintaining the sameexposed diaphragm area between the members for various relativepositions of the members.

2. A diaphragm assemblycomprising a housing having a cylindrical innerwall, a cylindrical cup member slidable in said housing ,in spacedrelation from said inner wall, a flexible diaphragm surrounding said cupmember andbridging the space between the member and housing, saiddiaphragm having inner and outer marginal portions adapted to engage thecup member and the cylindrical wall respectively and to roll from suchengaging position into bridging position between the housing and cupwhereby theeffective exposed area of the diaphragm between the housingand cup remains constant for all positions of the cup in the housingwhile being defined by different portions of the diaphragm.

3. In a pump including a'housing defining a suction chamber between theinlet and discharge sides of the pump in communication with the inletside of the pump, a relief valve in said housing betweensaid suctionchamber and discharge side of the pump, and adjustable means for loadingsaid relief valve, the improvements which comprise said housing having atubular portion depending in said suction chamber into spaced relationfrom said relief valve and said being spaced from the walls of cupmember slidably embracing said tubular portion and having a closed endbetween the adjustable loading means and,the relief valve, said loadingmeans urxi-nz theclosed end of said cup against the relief valve, aflexible diaphragm surrounding said cup member and looped between thecup member and the housing to bridge the space therebetween. said divthe housing and cup member for maintaining the same exposed diaphragmarea'between the housing and cup member for various relative positionsthereof.

' RUSSELL R. CURTIS.

to roll against one of then the other member as

